Among the listed RNAs, the one that is not directly involved in protein synthesis is pRNA.

Explanation:

• mRNA (Messenger RNA): This type of RNA carries the genetic information from DNA in the cell nucleus to the ribosomes in the cytoplasm, where it serves as a template for protein synthesis. mRNA directs the assembly of amino acids into specific polypeptide chains during translation.

• rRNA (Ribosomal RNA): Ribosomal RNA is a major component of ribosomes, the cellular machinery where protein synthesis occurs. It plays a structural and functional role within ribosomes by aiding in the binding of mRNA and tRNA during translation.

• tRNA (Transfer RNA): Transfer RNA is responsible for bringing specific amino acids to the ribosome during protein synthesis. Each tRNA molecule carries a specific amino acid and has an anticodon that pairs with the codon on the mRNA, ensuring that the correct amino acid is added to the growing polypeptide chain.

So mRNA, rRNA, and tRNA are directly involved in various stages of protein synthesis.